This is a multi-site study conducted to characterize standardized current perception threshold (CPT) and pain perception threshold (PPT) measures in complex regional pain syndrome (CRPS) patients and in healthy matched controls. The investigators hypothesize that evaluation of a patient's CPT and PPT measures will differentiate between CRPS patients and the healthy matched controls. The specific aims of this study are to study the impedance pattern of reflux episodes in normal volunteers in the fasting and postprandial states; and to assess whether esophageal impedance measurement improve the detection of Gastroesophageal reflux in subjects with known severe gastroesophageal reflux, as characterized by the presence of a columnar lined esophagus.